Rotary capping machines for applying pre-threaded closures have been known for some time. To insure that a pre-threaded closure is not applied too loosely or too tightly and to insure product integrity, rotary capping machines are equipped with capping heads dependent upon a torque coupling. The torque coupling controls the application of torque to the closures to insure that they meet packaging specifications. Various types of torque couplings exist in the art such as mechanical clutches and magnetic clutches.
A magnetic clutch typically consists of axially-opposed rings that are spaced apart by some distance. Each ring comprises an array of magnets mounted horizontally along each ring whereby the arrays of magnets on the opposing rings are in a facing relationship. In a magnetic clutch, one ring is typically fixed within a housing that is driven by a machine spindle and the other ring drives a capping head spindle that holds the closures. The magnetic field established between the arrays of magnets is the connection between the torque applied to the housing by the machine spindle and the torque applied to the closure by the capping head spindle. Axial distance between the opposing rings affects the torque transmitted by the magnetic clutch. Generally, a greater distance between the rings will decrease the magnetic interaction between the opposing arrays of magnets, and subsequently will decrease the amount of transmittable torque carried by the magnetic clutch. Any resistance torque applied to the magnetic clutch by the spindle beyond that of the transmittable torque causes the clutch to slip. Generally, spacer rings are used to maintain the distance between the opposing magnetic rings.
In addition to the clutch, each capping head also typically utilizes a telescoping lower/upper housing design, with the clutch located in the lower housing near the spindle. A spring is usually positioned between the upper housing and lower housing to help bias the housings away from each other and to exert a top-loading force on the closure to the container. The pre-load on the spring can be adjusted to vary the top-loading force on the closure, and this is often accomplished using a rotatable collar with a locking element, such as a set screw, that must be loosened to adjust the collar and tightened after the adjustment is made. Alternatively, the spring can be removed and replaced with another spring of a different stiffness.